Current environmental requirements dictate that coal and organic waste be burned to produce a gaseous or liquid derivative without the production of airborne sulphur oxides, nitrogen oxides, particulate matter, and without the problem of excessive residue ash. An obvious solution to this problem is to burn coal which itself contains a low content of sulphur, nitrogen, and particulate wastes. Such fuel is, however, in short supply and accordingly expensive, so only rarely can fuel with a desirable content be made available. More generally, a low grade coal or other carbonaceous material with a high content of particulate matter and sulphur is available.
A gas producing furnace utilizing low grade coal was shown and described in my previous U.S. Pat. No. 3,920,417 entitled, "Method of Gasifying Carbonaceous Material". In this patent a clean low BTU fuel gas was produced by reacting carbonaceous fuel with an oxidizer and steam in a fixed bed gasifier. The resulting reaction converted the carbonaceous fuel material to a molten slag and a gaseous effluent that was subsequently cooled and cleaned before it was directed to a place of use.